The present invention relates to a method and an apparatus for selecting a color and/or a transparency value of a computer graphics image.
Modern computer systems have become increasingly popular for utilisation in the production of high quality, full color images. An image consists of a number of pixels, and each pixel may be defined to be of a certain color and to have certain transparency aspects. Typically, a common format for representing a pixel is used. For example, one such common format is the Red, Green and Blue (RGB) format. In this format, each pixel may use 24 bits to represent the color, where eight bits are provided for each of the R, G and B components of the color of the pixel. With the 24-bit color definition, it is possible to represent over 16 million separate color. This effectively provides a high fidelity color space in which a large number of different colors can be represented with each color having only very minor variations in relation to the closest neighboring colors in the color space.
Still further, another eight bits may be used in the format to define a transparency aspect of each corresponding pixel. Eight bits of storage are also used for the transparency component, thereby resulting in a pixel storage size of 32 bits.
In order to choose a particular color within the gamut of all possible displayable colors in such a color space, a number of color selection tools have been used in the prior art. Most of these conventional tools rely on the display of the full color gamut of displayable colors in a compressed form. For a discussion of the utilisation of color in computer graphic images and various conventional color selection tools known in the art, reference is made to a standard text in the field such as Foley, Van Dam et.al, Computer Graphics Principles and Practice, 2nd Ed., Reading (Mass.): Addison-Wesley Publishing Company, Inc (1990), 574-603.
Disadvantageously, the provision of such a large number of colors to select from often results in confusion when such conventional color selection tools are used by graphic artists or the like to create computer graphic images. For example, when the full gamut of displayable colors is displayed in a small color selection area on a display, the results are such that it is typically extremely difficult for a person to distinguish between closely similar colors.
A conventional color selection system is disclosed in U.S. Pat. No. 5,254,978 that is used to create a palette of colorimetrically measured colors. The system is used to create and modify a color palette by selecting two end colors and interpellating between those two colors to form a linear blend. The operator may then select a color from the blend and add it to a palette of colors. Colors from the palette may be modified or deleted while the creation of new colors is carried out in a manner analogous to an artist's color wash. Thus, this conventional system is used to select or modify colors of a color palette by a user first selecting two separate colors to form a color wash of the color mixing region displayed on a video monitor. The wash or blend of the color mixing region is formed by interpellating colors in the CIELAB color space between the two user selected colors. The system is disadvantageous in that it requires a number of operations to be performed in order for an operator such as a graphic artist to select or create a new color. Firstly, the user must select two colors from the color palette to be used as the end points of the blend. Once the blend has been generated, the user must then again select a color from the blend to be added to the color palette. If the user were then to wish to modify the color further, the foregoing steps would have to be iterated once again. Thus, for realistic applications, this would consequentially be disadvantageous the large number of operations and the cumbersome nature of the technique for modifying colors would not lend itself to be in readily use by a user. A further disadvantage of this technique is that only a single blend is generated between the two selected colors and therefore does not enable a user to readily visualise the relationship between the colors of a chosen blend and those of other colors having different chromaticity in the neighbouring color space.